In a mobile communications system, a location update is a very important process. The location update includes a location area update and a routing area update. When a mobile terminal changes a location area, it needs to notify a network system to perform the location area update. When the mobile terminal changes a routing area, it needs to interact with the network system to perform the routing area update.
With the development of communications technologies, a third-generation mobile communications technology, 3G technology, for example, a technology such as wideband code division multiple access (WCDMA), code division multiple access 2000 (CDMA2000), and time division-synchronous code division multiple access (TD-SCDMA) has been widely applied. A network system based on the 3G technology is capable of transmitting voice and data information at the same time. However, a network system based on a second-generation communications technology, 2G technology, has undergone long-term construction and provides better coverage than a 3G network. Therefore, generally, an existing terminal device based on the 3G network supports a 2G network so as to satisfy that a user can use a wireless service at any location. For example, most 3G mobile phones are dual-mode mobile phones that support a 2G/3G network system, for example, WCDMA/global system for mobile communications (GSM) dual mode and TD-SCDMA/GSM dual mode.
The 2G network and 3G network can support a circuit switched (CS) domain service and a packet switched (PS) domain service at the same time. A common voice service and short message service are mainly provided by a CS domain, and a data service is mainly provided by a PS domain. However, a network, such as a GSM network, among 2G networks with complete coverage are suitable for the voice service, and the 3G network with an advanced system, such as a TD-SCDMA network, are suitable for the data service. Therefore, generally, an existing dual-mode mobile terminal is designed to support a PS service of the 3G network and a CS service of the 2G network at the same time. For example, a single-card dual-mode (e.g., GSM/TD-SCDMA dual-mode) mobile phone uses two sets of antennas, two sets of radio frequency modules, and two independent protocol stacks, GSM protocol stack and TD-SCDMA protocol stack, so that a 2G system and a 3G system can operate on and access one universal subscriber identity module (USIM) card at the same time.
Such a single-card dual-mode mobile terminal can camp on the 2G network and 3G network. A PS domain of the 3G network has a plurality of routing areas, whereas a CS domain of the 2G network has a plurality of location areas. During a location area update and routing area update, an existing mobile terminal separately executes update processes on the 2G network and the 3G network, which increases the workload and power consumption of the mobile terminal and finally affects the technical performance of the mobile terminal.